The handling and coating system described herein comprises a vacuum system, a transport system, and a plurality of processing stations. Also included, but not herein described, are various power supplies, water cooling means, gas handling means, and control systems.
It has become increasingly important to handle and transport on an individual basis thin substrates, such as semiconductor wafers and substrates for magnetic disks, from a cassette into, through, and out of a vacuum coating system and back into a cassette. Some recent developments in such systems are described in U.S. Pat. No. 4,311,427, "Wafer Transfer System" issued Jan. 19, 1982 to G. L. Coad, R. H. Shaw and M. A. Hutchinson, and assigned to the assignee of the present invention.
The above-referenced system has performed extremely well in important semiconductor wafer coating applications. With the emerging need for similar systems for processing and coating magnetic disk substrates, now of vital interest in computer memory applications, it has become apparent that certain modifications in various aspects of the system are needed for magnetic disk manufacture. Once effectively implemented, some of these modifications may be of benefit in semiconductor wafer processing as well.
One feature of the above-referenced system (U.S. Pat. No. 4,311,427) is that the thin substrates are held "on edge" in a vertical orientation, and are processed individually. Although both sides of the substrates are accessible for processing, only one side of the semiconductor wafer need be coated, with heating or cooling means being optionally applied to the back side of the wafer, for example. In the coating of magnetic disks, it is necessary to coat both sides of the substrate, and it is highly desirable to coat both sides simultaneously. A more symmetrical means of supporting the individual substrates during coating is therefore needed.
In some coating systems, substrates are transported from one processing station to another, and two or more different processes are carried out simultaneously (on different substrates or batches of substrates) in a common vacuum environment. In the semiconductor wafer processing system described in aforementioned U.S. Pat. No. 4,311,427, the wafers are in a common vacuum environment even though they are being individually processed. In at least some cases of magnetic disk processing it is desirable to avoid cross-contamination arising from widely differing processes simultaneously taking place at the various processing stations.
Many coating systems employ a substrate transport system. In most cases the various fixed and moving parts of the transport system become at least partially coated incidentally along with the substrates. The flaking of deposited material from the transport system, especially from the moving parts, leads to the generation of particulates, which may be detrimental to the substrates. This leads to the need for frequent servicing of the substrate transport system.
A technique known as RF (Radio Frequency) sputtering is frequently employed when the coating source material is an insulator or a poor conductor of electricity. When RF sputtering is used inside a vacuum enclosure, RF electric fields and currents tend to be established at various places within the enclosure. Leakage of RF out of the vacuum enclosure generally gives rise to radiation of RF power into the surrounding environment. To keep such radiation below acceptable levels, it is frequently necessary to apply RF shielding, grounding, and/or filtering means to each of the various mechanical motion feedthroughs, electrical feedthroughs, conduits, and apertures which penetrate the vacuum enclosure, whether or not a particular feedthrough or opening is directly associated with the operation of the RF sputtering process. In many cases only a small fraction of the feedthroughs and openings is so associated. If means were provided to eliminate the need for the shielding, etc., of those feed-throughs and openings not directly involved, significant savings in system complexity and cost could accrue.
In important applications to semiconductor wafer processing, systems with a fixed number of processing stations can be entirely satisfactory. Magnetic disk technology has not yet matured to a similar point. Flexibility in the number and type of individual processing stations is required.
In most semiconductor wafer applications, the required coatings are nonmagnetic and are deposited from magnetron sputter coating souces employing nonmagnetic targets. With magnetic disks, the major and critically important coatings are of magnetic material, and additional coatings of nonmagnetic materials may also be required. Present-day magnetron sputter coating sources have been designed to operate efficiently with nonmagnetic targets. Improved means for coating disks with magnetic materials are required if magnetic disk manufacturing systems are to be useful.
Magnetron sputter coating sources include cathode and anode structures, and are operated in an evacuated chamber back-filled with a sputter gas (typically argon at subatmospheric pressure). Voltage is applied between cathode and anode to establish a glow discharge. Positive ions formed in the space between anode and cathode impact a sputter target located on the cathode surface, ejecting (by sputtering) atoms of target material from the surface and near subsurface atomic layers of the target. These sputtered atoms deposit desirably on workpieces or substrates placed generally in line-of-sight of the sputter target. Sputtered atoms also deposit incidentially on various accessible surfaces, such as substrate holders, sputter shields, and chamber walls.
In using magnetron sputter coating sources, it is necessary to provide means for monitoring and controlling sputter gas pressure. Freshly-deposited films of many materials provide sites for physical adsorption (physisorption) of various gases, and also sites for chemical combination with (or chemisorption of) certain specific gases. The incorporation of excessive amounts of particular gases into the deposited films can result in contaminated coatings. It is therefore necessary to ensure adequately low levels of contaminant gases in the sputter gas atmosphere. This normally involves continuous pumping by a means which removes the sputter gas as well as the contaminant gases. A continuous inlet flow of sputter gas is therefore required to maintain the desired sputter gas pressure.
In vacuum coating systems generally, it is necessary to periodically replenish the supply of coating material, or to otherwise service the coating source or processing station. In most cases this necessitates shutting down the entire system or a major portion thereof and venting it to atmosphere. Returning the system to a clean operating condition introduces a significant time delay and interruption of production. Generally speaking, means for reducing system downtime associated with the servicing of processing stations can provide substantial benefits.
Accordingly, it is an object of the invention to handle and transport thin substrates in a manner that allows them to be individually coated and otherwise processed from both sides simultaneously.
It is also an object of the invention to provide means for avoiding cross-contamination among the various individual processing stations.
Another object of the invention is to minimize the incidental coating of the fixed and moving parts of the substrate handling and coating system.
Yet another object of the invention is to restrict the need for RF shielding, grounding, and/or filtering to those feedthroughs and openings directly associated with an RF process.
Still another object of the invention is to provide an improved means for controlling sputter gas pressure and purity.
A further object of the invention is to provide easy flexibility in building systems with differing numbers and types of individual processing stations.
It is an additional object of the invention to provide means for reducing system downtime associated with servicing individual processing stations.
Additional objects and features will become apparent from the ensuing description of the invention.